LRA, your Air Conditioner, and a DC to AC Inverter

If I have a backup style grid-tie solar system will my inverter start my Air Conditioner? Maybe, just depends on the Air Conditioners LRA rating and the inverter starting capacity. LRA means Locked Rotor Amperage. This is the inrush current that any motor has when it first starts up. The motor in this case is the compressor.

Here is an example that may e similar to many installations. (This would be what I am thinking of doing in my house anyway.)

Inverter would be a Xantrex XW 6048. It has a LRA surge rating of 52.5 amps. My current air conditioner, I think, is a 2.5 ton AC unit. Since I don’t know the LRA rating I used a new Goodman SEER 13 unit. This unit has a LRA rating of 49 amps.

Yes, the inverter would start the Air Conditioner. Or would it. Remember there are two other fans in a split system. A condenser fan and a blower fan. Both of these have a LRA ratings also. So in the end the chance of starting the entire system is low. Especially since you will have other power users running while the Air Conditioner is trying to turn on.

So I can’t run the entire house AC unit on the inverter. But can I run a small window unit. Yes, if the unit is 120V this inverter will not have a problem with it. That is because the inverter has a surge rating of 110 amps @ 120V. The house air conditioner was @ 240V.

If you wanted to run a window unit with an off the shelf inverter take the amperage while running and multiple by 7 to estimate the LRA draw. So if the running amps is 5. Then the estimated LRA would be 35 amps. Take the 35 amps x 120V = 4200 Watts. This would be the minimum size surge rating inverter you should buy.

Inverter-Driven Rotary Air Conditioners.

The nice thing about this type of air conditioner is the running amperage is very close to the Locked Rotor Amperage. The inverter in the AC unit starts the compressor out slowly and then ramps up to the desired speed. This means that if your windows unit or your central unit has this newer technology many more DC toAC inverters will do the job. The Xantrex XW line of inverter should have no issues getting it done. (FWIW – when I upgrade my AC I would like to go with an inverter type heat pump.)

We don’t do much large systems like that. Most customers who run solar from our store are using in remote cabins or such. , i always suggest for small cabins and such people stick with the smaller window units. We have been able to get most 5000btu units running on a 1500 watt true sine inverter. it would run smooth and start smooth. It only drew about 400 watts when running although the surge would get close to 1400 watts for about 6 seconds. I was just looking at my 4ton AC in my new house. Man it has a 96LRA rating. We keep having brownouts due to I think improperly size feed cable. They used 1/0 aluminum to span 150 + feet. Seems small to me.